More epidemiologic data are needed on the relation of background-level exposure to man-made chemicals with short half-lives to fetal and child development. The embryonic and fetal stages of development are periods of heightened susceptibility to effects of xenobiotics. For xenobiotics with short half-lives, characterizing exposure well has been a challenge in the past. Multiple urine specimens are the approach of choice for assessing exposure to such agents. Recent data suggest that background-level of exposure of pregnant women to nonpersistent pesticides can result in impaired neurodevelopment in offspring. We seek to increase our capacity to study the relation of background-level exposure to chemicals with short half-lives to pregnancy outcomes and child development. To achieve this goal we supported collection of multiple urine specimens during pregnancy in the Generation R study (described below). The plan was to support collection of urine 3 times during pregnancy for the mothers of 2,500 children in the cohort. Generation R is an ongoing prospective study of 10,000 children who will be followed from early fetal life to young adulthood, and aims to study how factors and events during pregnancy and early childhood can affect growth, development, and health in later life. All pregnant women in a specific section of Rotterdam who gave birth between June 2002 and June 2006 were invited to participate, together with their partner. This study was set up by the Erasmus Medical Center. The multidisciplinary characterization of the cohort, starting in early pregnancy, has produced a database containing biological, medical, genetic, psychological and community-related data which can be used to address a wide spectrum of research questions. The research questions have been subdivided as growth and physical development, cognition and behavior, illnesses and accidents, and utilization of health care resources. The advantage to studying this cohort, e.g., over the Norway Mother and Child Cohort Study, is that we will have multiple urine specimens, including one during the first trimester, enhancing our ability assess exposures, especially during organogenesis. Furthermore, the outcome assessment in the Generation R cohort is more intensive and standardized than in Norway. In February of 2004, NIEHS support enabled an increase in the number of urine specimens collected from each pregnant woman from 1 to 3 (at 12, 20, and 30 weeks of gestation). As each pregnant woman presents for an ultrasound examination of her fetus, she provides a spot urine specimen that is divided into three 20ml aliquots and frozen at -20 degrees C in polypropylene containers. Two of these aliquots are reserved for collaborative studies with NIEHS. Our primary interest is in women with a complete set of three urines. Enrollment is now complete. We have a complete set of 3 urines for 2,025 women, 2 urines for 970 women, and 1 urine for 356 women. We had 100 third trimester urine specimens sent to a laboratory to check the levels of exposure in this population. The laboratory results were published in previous years. With a few exceptions, the levels of phthalates, nonpersistent pesticides, and bisphenol A were similar to those reported in other populations in developed countries. The levels of total dimethyl alkyl metabolites (of organophosphate pesticides) were higher than in the CHAMACOS study (Salinas, California); total diethyl metabolites were similar. Levels of bisphenol A were about the same as in the Calafat et al. NHANES report from 2005. Thus, examinations of health outcomes in relation to these contaminants will be worthwhile. Last years progress: To study organophosphate pesticide metabolite concentration in relation to neurodevelopment, urine specimens were analyzed (three urine specimens from 800 women, and one urine specimen per child). This year, we examined the association between analytes and ADHD symptoms in childhood, maternal thyroid hormone levels, and fetal growth as measured by repeated ultrasounds in pregnancy. A postdoctoral fellow in the Netherlands, supported by NIEHS, is now examining organophosphate pesticide metabolite concentrations in relation to other neurodevelopmental endpoints and beginning investigation of mixtures of organophosphate pesticide metabolites and other environmental exposure biomarkers (phthalate metabolites, bisphenols) in association with various endpoints.